UNIVERSITY  OF   CALIFOBNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


THE  PEACH  TWIG-BORER 

(Anarsia  lineatella  Zeller) 


BY 

WILLIS  P.  DURUZ 


BULLETIN  No.  355 

March,  1923 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1923 


David  P.  Barrows,  President  of  the  University. 

EXPEEIMENT  STATION  STAFF 

HEADS  OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

E.  J.  Wickson,  Horticulture  (Emeritus). 

,  Director  of  Eesident  Instruction. 

C.  M.  Haring,  Veterinary  Science;  Director  of  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 

C.  B.  Hutchinson,  Plant  Breeding;  Director  of  the  Branch  of  the  College  of 

Agriculture. 
H.  J.  Webber,  Citriculture;  Director  of  Citrus  Experiment  Station. 
William  A.  Setchell,  Botany. 
Myer  A.  Jaffa,  Nutrition. 
Ealph  E.  Smith,  Plant  Pathology. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
James  T.  Barrett,  Plant  Pathology. 
Walter  Mulford,  Forestry. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Eeed,  Plant  Physiology. 
L.  D.  Batchelor,  Orchard  Management. 
W.  L.  Howard,  Pomology. 
*Frank  Adams,  Irrigation  Investigations. 

C.  L.  Eoadhouse,  Dairy  Industry. 
E.  L.  Adams,  Farm  Management. 

W.  B.  Herms,  Entomology  and  Parasitology. 
John  E.  Dougherty,  Poultry  Husbandry. 

D.  E.  Hoagland,  Plant  Nutrition. 
G.  H.  Hart,  Veterinary  Science. 

L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 

DIVISION  OF  POMOLOGY 
W.  L.  Howard  W.  P.  Duruz 

W.  P.  Tufts  L.  C.  Barnard 

E.  L.   OVERHOLSER  I/.    H.    DAY 

A.  H.  Hendrickson  J.  L.  Stahl 

F.  W.  Allen  C.  L.  Austin 
J.  P.  Bennett  M.  J.  Heppner 

G.  L.  Philp 

*  In  cooperation  with  Division  of  Agricultural  Engineering,  Bureau  of  Public  Roads,  U.  S. 
Department  of  Agriculture. 


THE  PEACH  TWIG-BORER 

(Anarsia  lineatella  Zeller) 

By  WILLIS  P.  DURUZ 


CONTENTS 

PAGE 

Introduction 419 

Review  of  Literature 421 

Description  of  the  Insect 424 

Systematic  Position 424 

Names  of  the  Insect 425 

Life  History 426 

The  Larvae 426 

The  Pupae 429 

The  Adults 430 

The  Eggs 431 

Larvae  of  Second  Generation 434 

Larvae  of  Third  Generation 434 

Hibernation  of  Last  Brood  of  Larvae 435 

Parasitism 437 

Life  History  Experiments 438 

Evidences  of  a  Second  Generation 438 

Evidences  of  a  Third  Generation 442 

Spraying  Experiments  1921 443 

Details  of  the  Experiments 444 

Discussion  of  Results 445 

Spraying  Experiments  1922 447 

Details  of  the  Experiments 447 

Discussion  of  Results 455 

Conclusions 459 

Recommendations 460 

Summary 461 

Acknowledgments 462 

Literature  Cited 462 


INTRODUCTION 

The  peach  twig-borer  or  peach  worm,  Anarsia  lineatella  Zeller,  is 
an  Old  World  insect,  probably  coming  to  this  country  many  years 
ago  on  fruit  trees  from  Asia.  It  has  become  a  serious  pest  in  this 
country  and  causes  great  loss  every  year.  Records  show  that  it  is 
present  in  at  least  fifteen  states,  including  California,  Colorado,  Dela- 
ware,  District   of   Columbia,   Georgia,    Illinois,   Idaho,   New   Jersey, 


420  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

New  York,  Maryland,  Mississippi,  Oregon,  Texas,  Virginia,  and 
Washington,  as  well  as  in  Canada,  and  probably  occurs  the  world  over, 
wherever  its  host  plants  are  grown. 

It  is  particularly  serious  on  the  Pacific  Coast,  and  in  California 
is  one  of  the  three  or  four  most  destructive  insects  found  on  stone 
fruits.  It  attacks  not  only  the  peach,  but  the  almond,  apricot,  nectar- 
ine, plum  and  prune.  Every  season  severe  damage  is  done  to  the  buds 
and  young  terminal  shoots,  particularly  on  trees  one  to  four  years  old, 
and  still  greater  is  the  loss  by  injury  to  the  fruit.  It  is  estimated  that 
in  California  the  loss  averages  from  ten  to  forty  per  cent  of  the 
entire  crop  and  amounts  to  over  one  million  dollars  annually. 

At  various  times  since  the  discovery  of  the  peach  twig-borer, 
investigators  have  studied  its  habits  and  attempted  its  control.  Ex- 
periments conducted  in  1902  by  Warren  T.  Clarke,5*  in  Placer  County 
proved  conclusively  that  this  insect  could  be  controlled  by  a  home- 
made lime,  salt,  and  sulfur  spray  applied  as  the  buds  were  swelling. 
Many  years  of  experience  seemed  to  prove  the  effectiveness  of  this 
treatment.  Gradually  the  commercial  preparation  of  lime-sulfur 
with  the  salt  omitted,  displaced  this  homemade  mixture  and  became 
the  standard  remedy  for  spraying  against  the  peach  twig-borer. 

During  the  last  three  or  four  years,  however,  some  doubt  has  arisen 
as  to  the  advisability  of  using  lime-sulfur  at  all,  particularly  on 
apricot  trees,  for  fear  of  injuring  the  fruit.  Many  fruit  growers 
in  California  have  also  questioned  the  efficacy  of  lime-sulfur  as  a 
control  for  the  peach  twig-borer,  because  they  have  observed 
considerable  injury  from  this  insect  even  when  this  spray  was  applied 
in  the  recommended  manner.  It  has  been  felt,  too,  that  additional 
spray  materials  ought  to  be  tested  out,  especially  on  host  plants  other 
than  the  peach. 

Moreover,  there  has  been  much  controversy  among  entomologists 
regarding  the  life  history  of  the  insect.  Some  authorities  have  be- 
lieved that  there  are  from  two  to  four  generations  a  year,  while  the 
observations  of  others  convinced  them  that  there  is  but  one  irregular 
brood  which  extends  over  the  entire  season. 

All  this  uncertainty  and  the  great  economic  importance  of  the 
insect  made  a  new  investigation  of  the  peach  twig-borer  necessary. 
It  was  desirable,  first,  that  the  life  history  and  habits  of  the  insect 
be  carefully  observed,  and  second,  that  a  satisfactory  means  of  com- 
bating it  be  found.  This  bulletin  is  a  report  of  three  seasons'  study 
and  experiment  dealing  with  the  points  above  mentioned  as  well  as 
with  other  miscellaneous  factors.     The  observations  and  experiments 


*  Reference  to  literature  cited  on  page  462. 


Bulletin  355]  THE  PEACH  TWIG-BORER  421 

were  conducted  at  Davis,  Esparto,  and  Winters,  Yolo  County ;  Vaca- 
ville,  Solano  County;  and  Auburn,  Newcastle,  Loomis,  and  Penryn, 
Placer  County. 

Certain  of  the  observations  and  results  herein  reported  agree  with 
the  findings  of  some  investigators,  but  disagree  with  those  of  others. 
Some  hitherto  unnoted  habits  of  the  insect  have  been  observed  and 
its  life  history  at  several  places  carefully  determined.  Certain  details 
regarding  remedial  measures  have  been  learned  which  make  the 
control  of  this  insect  more  complete  and  satisfactory  by  permitting 
the  fruit  grower  to  attack  it  at  three  or  four  different  stages.  Other 
miscellaneous  matters  have  been  discovered  that  lead  to  advice  which, 
if  followed,  will  prove  helpful  in  preventing  serious  injury  from  this 
pest  in  the  future. 

EEVIEW   OF  LITERATURE 

A  brief  review  of  the  important  literature  of  previous  writers  is 
here  presented  to  show  the  development  and  accumulation  of  informa- 
tion relating  to  the  peach  twig-borer. 

The  first  published  account  of  the  peach  twig-borer  was  the 
original  description  by  Zeller  in  Germany  in  1839. 37  Clemens6  in 
1860  described  the  same  insect  in  this  country,  assigning  it  to  a 
different  species,  however,  and  doubtfully  referring  it  to  the  genus 
Anarsia  (Anarsia  pruinella).  But  in  18727  he  identified  it  with  the 
insect  described  by  Zeller.  Riley  also  obtained  specimens  of  the 
same  moth  from  peach  twigs,  and  on  submitting  samples  to  Zeller, 
they  were  pronounced  identical  with  the  European  insect. 

In  1872  Saunders31  described  an  insect  attacking  the  crown  and 
root  of  the  strawberry  and  believed  it  to  be  the  peach  twig-borer. 
This  theory  was  shared  by  subsequent  writers  until  Cordley11  in 
Oregon  in  1897  pointed  out  the  fact  that  the  peach  twig-borer  and 
the  strawberry  crown-borer  were  distinct  insects. 

In  July  1872  Glover17  reported  the  peach  twig-borer  as  occurring 
in  Maryland  and  Virginia  and  doing  damage  for  the  first  time  in 
the  United  States.  He  described  the  nature  of  the  injury  and  sug- 
gested cutting  off  the    withered  shoots  in  May  and  June. 

Comstock8  in  1878  briefly  described  the  twig-boring  habit  of  the 
larvae  of  this  insect  and  the  pupation  of  a  second  generation  on  the 
peach. 

Lintner22  in  1882  gave  a  bibliography  and  quotations  of  previous 
writers  and  further  described  the  habits  of  the  insect.  He  reported 
it  as  occurring  in  eight  different  localities  in  New  York  State  and 


422  UNIVERSITY    OF    CALIFORNIA— EXPERIMENT    STATION 

referred  to  the  existence  of  a  chalcid  parasite  {Copidosoma  of  Ratze- 
burg)  on  the  pupa.  He  also  recommended  cutting  off  the  wilted  shoots 
in  May  and  June. 

Klee21  in  1888  described  the  damage  caused  by  the  twig-borer  to 
various  plants,  including  strawberries  in  California.  He  stated  that 
it  was  subject  to  parasites,  which  might  account  for  its  disappearance 
in  some  localities.  He  recommended  scraping  off  the  rough  bark  of 
trees  and  removing  wilted  young  twigs,  as  well  as  guarding  against 
introducing  the  pest  on  fruit  boxes  into  non-infested  districts. 

Coquillett10  in  1891,  referred  to  the  working  of  an  insect  suspected 
to  be  Anarsia  lineatella  in  Kern  County  on  trees  brought  from  Ala- 
meda, California.  He  described  the  working  of  the  insect  in  terminal 
shoots.  Fully  eight  hundred  apricot  trees  were  reported  attacked, 
from  four  to  six  of  the  youngest  twigs  being  destroyed  on  each  tree. 
Spraying  with  Paris  green  (1  pound  to  180  gallons  of  water)  was 
reported  to  be  an  effective  control  measure. 

The  next  work  of  economic  value  was  that  of  Ehrhorn,  reported 
by  Craw13  in  1893.  Results  of  Ehrhorn 's  investigations  in  the  Santa 
Clara  Valley,  California,  showed  that  the  insect  winters  in  the  early 
larval  stages  in  hollow  chambers  in  crotches  of  the  branches.  Eggs 
of  the  last  brood  are  placed  in  the  fall;  the  larvae  hatch  and  grow 
very  slowly  at  the  point  indicated  and  construct  chambers  for  passing 
the  winter.  When  new  growth  starts  in  the  spring  they  leave  their 
burrows  in  the  bark  and  enter  the  new  shoots.  The  later  brood  works 
in  the  fruit.  Remedies  suggested  were;  coal  oil  or  resin  solution,  or 
lime-sulfur-salt  mixture  sprayed  in  January  or  February.  Clipping 
off  the  wilted  shoots  was  also  suggested.  He  considered  the  trial  of 
parasites  advisable. 

In  1898  Gossard19  briefly  described  the  insect's  habits  and  the 
injury  it  did.  Kerosene  emulsion  was  recommended,  but  its  effective- 
ness was  doubted. 

Marlatt23  in  1898  published  the  fullest  account  of  the  peach  twig- 
borer  up  to  that  time.  He  thoroughly  reviewed  the  work  of  previous 
investigators,  including  descriptions  of  the  insect,  its  habits,  life 
history,  and  control  measures.  He  told  of  a  minute  parasitic  native 
mite  (Pediculoides  ventricosus)  and  a  chalcid  parasite,  alluded  to 
by  Comstock8  and  later  described  by  L.  0.  Howard  as  Copidosoma 
variegatum.  A  new  parasite  was  reported  from  material  submitted 
by  Ehrhorn  and  identified  by  Ashmead  as  Oxymorpha  livida.  The 
remedies  advised  were  clipping  off  the  wilted  shoots  in  May  and 
spraying   with   kerosene    emulsion   in   January    or    February.      The 


Bulletin  355]  THE  PEACH  TWIG-BORER  423 

possibility  of  control  by  arsenicals  in  the  fall  and  spring  was  also 
suggested,  but  at  the  same  time  doubt  was  cast  upon  their  effective- 
ness. 

Unfortunately  the  work  done  by  Marlatt23  was  not  conducted 
under  natural  field  conditions  and  in  many  respects  does  not  agree 
with  observations  made  in  California.  Likewise  other  eastern 
observations  have  been  fragmentary  and  require  verification  before 
being  used  on  the  Pacific  Coast  as  a  basis  for  a  plan  of  control. 

The  best  work  on  the  control  of  the  twig-borer  in  California  was 
done  by  Clarke5  who  published  his  results  in  1902.  Clarke  reported 
observations  on  the  activity  of  the  insect  and  gave  the  results  of 
spraying  experiments  in  Placer  County.  Many  points  in  the  life 
history  were  cleared  up,  several  observations  being  at  variance  with 
previous  published  accounts.  Conclusions  drawn  from  the  experi- 
ments warranted  the  recommendation  to  spray  with  lime-sulfur-salt 
mixture  at  the  time  the  buds  are  swelling. 

Piper25  in  1905  writing  of  ' '  Orchard  Enemies  of  the  Pacific  North- 
west," includes  the  peach  twig-borer  as  an  important  pest.  He  tells 
of  the  insect  being  "  usually  noted  in  late  varieties  of  peaches,  the 
earlier  ones  being  exempt  as  a  rule. ' '  The  type  of  injury  and  extent 
of  damage  is  described.  Piper  states,  "lime-sulfur-salt  mixture 
shows  no  appreciable  effect."  Kerosene  emulsion  proved  the  most 
reliable  remedy. 

In  1907  Taylor32  working  in  Colorado  made  the  following  sum- 
mary of  spraying  experiments:  "Former  recommendations  for  the 
control  of  this  insect  have  been  for  spring  applications  of  lime  and 
sulfur  washes.  This  has  in  fact  been  a  most  successful  treatment, 
but  the  use  of  lead  arsenate  against  the  twig-borer  of  the  peach  is 
destined  to  meet  with  equal  popularity  when  its  efficiency,  cost,  and 
convenience  of  preparation  and  application  are  considered."  Taylor's 
counts  showed  97  per  cent  benefit  from  spraying  with  arsenate  of 
lead,  as  against  90  per  cent  with  lime-sulfur,  the  spray  being  applied 
as  the  blossoms  were  showing  pink. 

Yothers36  in  1914  held  the  opinion  that  the  "regular  San  Jose 
scale  spraying  (either  with  lime-sulfur  or  crude  oil  emulsion)  would 
reduce  the  work  of  the  peach  twig-borer  to  a  minimum  in  the  state 
of  Washington. 

In  1915  Wilson35  published  a  very  complete  account  of  this  insect 
in  Oregon.  He  reviewed  its  life  history  and  admitted  that  the  ques- 
tion of  the  number  of  generations  per  year  in  Oregon  was  puzzling. 
At  Corvallis  only  a  single  generation  was  found,  while  in  eastern 
and  southern  Oregon  two  or  three  generations  appeared.     Results 


424  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

of  a  series  of  spraying  experiments  were  tabulated,  showing  that 
when  applied  in  April,  lime-sulfur,  1-12,  in  combination  with  arsen- 
ate of  lead,  2-50,  gave  almost  perfect  control.  "Black  Leaf  40," 
1-2000,  with  lime-sulfur,  1-12,  also  gave  very  high  control,  as  did 
arsenate  of  lead,  2-50,  with  "Black  Leaf  40,"  1-2000.  Arsenate  of 
lead  and  "Black  Leaf  40"  alone  also  gave  good  control. 

Essig14  in  1915  in  his  publication  on  "Injurious  and  Beneficial 
Insects  of  California, ' '  gives  a  most  complete  summary  of  the  present 
information  on  the  peach  twig-borer.  The  life  history,  nature  of 
work,  distribution,  food  plants,  natural  enemies,  and  control  are  all 
very  thoroughly  discussed.  Essig  shared  the  opinion  of  G.  P.  Weldon 
that  the  insect  had  but  one  uneven  brood  a  year.  The  control  sug- 
gested was  "a  thorough  application  of  lime-sulfur  spray  when  the 
buds  begin  to  swell." 

Howard's  and  Home's20  observations  in  1920  in  experiments  with 
brown  rot  showed  that  the  peach  twig-borer  was  almost  completely 
controlled  with  commercial  lime-sulfur  1-10,  and  by  dry  lime- 
sulfur,  12-50.  They  further  remark,  however,  "This  was  especially 
true  where  trees  were  sprayed  twice  before  they  came  into  bloom. 
Spraying  after  the  trees  came  into  bloom  with  either  of  the  lime-sul- 
furs  had  little  effect  against  the  borer.  Bordeaux  mixture  and  oil 
sprays  afforded  no  protection  against  the  insect." 

In  1921  Wakeland33  called  attention  to  the  seriousness  of  the 
peach  twig-borer  in  Idaho  on  peaches  and  prunes.  He  recommended 
spraying  with  lime-sulfur  at  the  time  the  buds  are  swelling  and 
doubted  that  a  combination  of  lime-sulfur  and  arsenate  of  lead 
would  prove  worth  the  additional  expense.  Although,  admitting 
cases  where  such  sprays  brought  the  desired  results,  arsenate  of  lead 
alone,  he  states,  "is  likely  to  prove  unsatisfactory." 

DESCRIPTION  OF  THE   INSECT 

Systematic  Position. — The  peach  twig-borer  belongs  to  the  order 
Lepidoptera,  and  has  been  assigned  to  the  family  Gelechiidae2. 

The  original  description  of  the  genus  Anarsia  and  the  species 
lineatella  as  given  by  Zeller37  is  quoted  below : 

"17.  Anarsia  Zell.  Palpen  des  Mannchens  wie  bei  Ateliotum,  die 
des  Weibchens,  dessgleichen  die  Kopfhaare,  die  Junge,  der  Pliigelbau 
u.  beider  Geschlechter  wie  bei  Ypsolophus. 

1.  Decolorella  Zell — grosser  als  Anchin.  bicost.;  die  Vorderfl.  blass 
lehmgelblich,  an  den  Gegenrandern  aschgrau,  im  Mittelraume  mit  eini- 
gen  Langsreihen  schwarzer  Punctehen. — I.  M.  aus  Sicilien. 


Bulletin  355]  THE  PEach  TWIG-BORER  425 

2.  Spartiella  Schr.  Grosse  von  Ypsol.  striatellus ;  die  Vorderfl.  aschgrau, 
braunlich  unrein,  mit  braunlichen  Schragstrichelchen  am  Vorderrande. 
Gegen  30  M.  und  W.  erhielt  ich  im  Juni  aus  Kaupen  von  Genista  tinct. 

3.  Lineatella  FK.  von  2  nur  dadurch  verschieden,  dass  sie  schwarze, 
ungleichmassige  Langstriche  im  Mittelraume  hat.  I  M.  aus  Oesterreich,  in 
FBs  Sammlung. ' ' 

Clemens6  describes  the  same  insect  thus : 

"Head  and  face  pale  gray;  thorax  dark  gray.  Labial  palpi  dark 
fuscous  externally,  and  pale  gray  at  the  end;  terminal  joint  gray, 
dusted  with  dark  fuscous.  Antennae  grayish,  annulated  with  dark 
brown.  Fore  wings,  gray,  dusted  with  blackish-brown,  with  a  few 
blackish-brown  spots  along  the  costa,  the  largest  in  the  middle,  and 
short  blackish-brown  streaks  on  the  median  nervure,  subcostal  in  the 
fold,  and  one  or  two  at  the  tip  of  the  wing;  cilia  fuscous  gray.  Hind 
wings   fuscous   gray;    cilia   gray   tinted  with  yellowish." 

The  larva  has  been  decribed  by  Saunders31  as  follows : 

"The  head  is  rather  small,  flattened,  bilobed,  pale  brownish-yellow, 
darker  in  color  about  the  mouth,  and  with  a  dark  brown  dot  on  each 
side.  The  body  above  is  semitransparent,  of  a  reddish-pink  color,  fading 
into  dull  yellow  on  the  second  and  third  segments;  anterior  portion  of 
second  segment  smooth  and  horny-looking,  and  similar  in  color  to  the 
head.  On  each  segment  are  a  few  shining  reddish  dots  (yellowish  on 
the  anterior  segments),  or  faintly  elevated  tubercles,  from  each  of 
which  arises  a  single,  very  fine,  yellowish  hair,  invisible  without  a 
magnifying  power;  these  dots  are  arranged  in  imperfect  rows,  a  single 
one  across  the  third,  fourth  and. terminal  segment,  and  a  more  or  less 
perfect  double  row  on  the  remaining  segments.  The  under  surface  is 
of  a  dull  whitish  color,  becoming  faintly  reddish  on  the  hinder  segments, 
with  a  few  shining  whitish  dots;  those  on  the  fifth,  sixth,  eleventh  and 
twelfth  segments,  being  arranged  in  transverse  rows,  in  continuation 
of  those  above.  The  feet  and  prolegs  are  yellowish-white,  the  former 
faintly  tipped  with  dark  brown.  It  spins  a  slight  silken  thread,  by 
which  it  can  suspend  itself  for  a  time,  at  a  short  distance  from  its 
place  of  attachment. ' ' 

Names  of  the  Insect. — The  peach  twig-borer  is  known  scientifically 
as  Anarsia  lineatella  Zeller.  There  are  many  common  names  applied 
to  it,  including  the  following:  peach  worm,  bud  worm,  peach  moth, 
bud  moth,  peach  and  prune  twig-borer,  and  prune  and  peach  twig 
miner.  The  simple  name  of  twig-borer  is  liable  to  be  confusing  with 
the  coleopterous  branch,  and  twig-borer  (Polycaon  confertus  Leconte). 
In  California  " peach  twig-borer"  is  the  name  recognized  by  au- 
thorities. 


426 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


LIFE  HISTOEY 

The  Larvae. — In  central  and  northern  California  the  larvae  may 
be  found  in  the  hibernating  chambers  or  hibernaculae  from  September 
1  to  March  15.  The  presence  of  hibernating  larvae  would  be  hard 
to  detect  were  it  not  for  the  presence  of  small  reddish  brown  chimneys, 
or  tubes  sticking  up  from  the  surface  of  the  bark   (fig.  1).  These 


Fig.  1. — Crotch  showing  chimney  of  hibernating  peach  twig -borer.     (Enlarged.) 


chimneys  consist  of  tiny  pieces  of  bark  fastened  together  with  silk. 
They  are  constructed  by  the  burrowing  larvae  always  on  the  upper 
surfaces  in  the  crotches  of  the  younger  branches.  They  are  rarely 
found  in  the  crotches  of  branches  that  are  more  than  three  years  of 
age.  As  Clarke5  states,  there  seems  to  be  something  in  the  composi- 
tion of  the  tissue  at  these  points  which  makes  them  a  favorable  loca- 
tion for  winter  quarters. 

On  cutting  into  one  of  these  chambers  it  will  be  found  that  they 
extend  well  beneath  the  bark  into  the  cambium  layer.  The  burrow  is 
from  two  to  three  times  longer  than  the  larva  within  it  and  has  a  silk 
lining  which  projects  well  up  into  the  tube  above  (fig.  2).  This 
silk  lining  affords  protection  from  the  weather  and  apparently  from 
some  spray  materials.  The  exact  function  of  this  peculiar  tube  is 
not  definitely  known. 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


427 


The  larvae  pass  the  winter  months  in  these  burrows  apparently 
without  feeding,  as  they  do  not  increase  perceptibly  in  size.  With 
the  warm  weather  of  spring  they  become  active  and  work  their  way 
out  of  the  cells.  The  time  of  emergence  seems  to  be  correlated  with 
the  sap  flow  of  the  tree.  On  almond  trees  which  start  growth  relative- 
ly early  the  larvae  seem  to  become  active  before  they  do  on  peach 
or  plum  trees  in  the  same  locality.  This  time  is  usually  when  the 
buds  on  the  tree  are  swelling.     Freshly  opened  hibernaculae  were 


Fig.  2. — Burrow  laid  open,  showing  the  worm  in  its  winter  quarters  under  the 
outer  bark.     (After  Ciarke.) 


found  on  almond  trees  at  Davis,  Yolo  County,  March  2,  while  at 
Auburn,  Placer  County,  larvae  were  found  emerging  on  plum  trees  as 
late  as  March  22. 

Upon  leaving  the  hibernation  chambers,  the  larvae  crawl  about 
for  a  couple  of  days,  then  go  to  the  base  of  a  bud  or  in  between  the 
expanding  leaves  and  begin  to  eat  their  way  down  and  into  the  tips 
of  the  twigs,  gaining  in  size  as  they  feed.  Frequently  the  larvae 
merely  bore  into  a  bud,  then  withdraw,  and  attack  another.  This 
occurs  when  they  attack  newly  placed  scions  of  grafts;  they  eat  off 
every  bud  on  a  scion,  but  do  not  go  into  the  harder  tissue.  The  most 
usual  manner  of  attack,  however,  is  to  bore  into  the  pith  of  a  chosen 
shoot,  taking  a  downward  course,  eating  all  of  the  interior,  and 
leaving  only  the  bast  and  wood  fibres  to  hold  the  twig.     This  causes 


428 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


the  characteristic  wilting  of  the  twig  (fig.  3),  which  later  dries  up 
and  breaks  off.  When  the  larvae  reach  the  harder  wood  they  bore 
their  way  out,  leaving  a  circular  exit  hole  in  the  side  of  the  twig 
(fig.  4).  Each  larva  may  attack  several  shoots  in  this  way  and  thus 
multiply  the  injury. 


Fig.  3. — Shoots  and  twigs  showing  characteristic  wilting  caused  by  larvae  of 
the  peach  twig-borer. 


Fig.  4. — Base  of  almond  twig  showing  exit  hole  of  larva.     (Enlarged.) 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


429 


By  destroying  the  terminal  growth  of  a  shoot,  serious  injury  is 
done,  particularly  to  nursery  stock  and  young  trees.  New  cells  must 
be  formed  and  length  growth  revived  at  great  expense  of  energy  and 
stored  plant  food.  Three  or  four  larvae  may  seriously  devitalize  or 
even  completely  destroy  a  young  tree  by  repeated  attacks  on  the 
new  growth.  The  attacks  are  not  so  injurious  to  older  trees  (five 
years  and  upward),  and  do  not  prove  fatal. 

It  has  been  the  theory  of  some  entomologists  that  later  emerging 
larvae  of  the  first  or  winter  generation  attack  the  developing  fruit. 


Fig.  5. 

pupating. 


-Portion  of  bark  showing  silken  web  spun  over  place  where  larva  is 


This  theory  was  disproved  by  experimental  counts  (p.  441)  which 
showed  that  all  the  larvae  emerge  at  nearly  the  same  time  and  feed 
on  buds  and  shoots  first,  then  give  rice  to  second  and  third  generation 
larvae  which  feed  on  the  fruit  or  twigs  or  both.  The  fourth  genera^^r 
tion  of  larvae  do  not  feed,  but  at  once  begin  to  construct  hibernaculae^ 
in  which  they  pass  the  winter,  and  these  constitute  the  first  generation 
larvae  of  the  following  season. 

The  Pupae. — When  the  larvae  are  full-grown  and  ready  to  pupate, 
they  seek  a  secluded  spot  in  old  pruning  wounds,  in  curls  of  bark, 
or  in  rough  crevices  on  the  main  trunk  of  the  tree  and  occasionally  in 
curled  leaves.  The  larva  invariably  spins  a  characteristic  silk  web 
over  the  entrance  to  the  place  of  concealment  (fig.  5).  By  the  last 
of  April  at  Davis,  all  of  the  larvae  had  disappeared  from  the  burrows 
in  the  twigs  and  many  were  found  pupating  in  the  various  places 
just  mentioned. 


430 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  larva  forms  an  extremely  flimsy  web  out  of  a  few  threads 
of  whitish  silk,  which  serve  only  to  hold  the  pupa  in  place,  and  not  for 
protection.  The  abdomen  of  the  pupa  is  attached  to  this  support  by 
a  little  button  of  silk. 

The  pupa  or  chrysalis  (fig.  6)  is  about  six  millimeters  long,  rather 
broad,  and  dark  brown  in  color.  The  segments  on  the  abdomen  are 
pronounced,  but  only  the  last  three  are  flexible,  which  accounts  for  a 
slight  twitching  movement  when  the  pupa  is  held  in  the  hand. 


Fig.  6. — Pupae  of  the  peach  twig-borer, 
curled  leaves.     (Enlarged.) 


Occasionally  pupation  takes  place  in 


The  pupation  period  in  the  case  of  the  first  generation  lasts  about 
fourteen  days.  With  the  second  generation  the  time  is  much  shorter, 
being  only  two  to  four  days,  while  with  the  third  generation  it  varies 
from  7  days  in  Esparto,  to  20  days  in  Newcastle,  California.  This  is 
due  apparently  to  climatic  conditions  in  the  different  sections. 

The  Adults. — The  adult  moths  of  the  first  generation  emerge  be- 
tween May  1  and  May  15,  according  to  the  climatic  factors.  Adults 
of  the  second  generation  emerge  in  general  from  August  1  to  August 
10.  The  last  brood  of  moths  appears  about  the  first  week  in  Sep- 
tember. 

The  moths  are  seldom  observed,  being  very  small  and  extremely 
quick  in  their  movements  and  flying  with  great  rapidity  when  dis- 
turbed in  their  hiding  places.  They  are  from  ^4  to  %  inch  long  and 
dark  steel  gray  in  color  (fig.  7).    It  is  interesting  to  note  that  Clarke5 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


431 


was  unable  to  trap  these  moths  by  lantern  traps  even  when  present 
in  large  numbers,  although  scores  of  other  closely  related  species 
were  easily  enticed. 

The  Eggs. — Eggs  of  the  first  brood  of  moths  are  deposited  on  the 
twigs  (fig.  8),  the  second  and  third  broods  on  the  fruits  or  twigs  and 


Fig.  7. — Adult  moths  of  the  peach  twig-borer.      (Enlarged.) 


Fig.  8. — Eggs  of  peach  twig-borer  in  position  on  twig.      (After  Clarke.) 


432  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  9a. — Fruit  showing  damage  from  peach  twig-borer.  Note  two  distinct 
types  of  injury.  The  upper  picture  shows  working  around  the  pit  and  the  lower 
picture  shows  surface  injury. 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


433 


the  fourth  apparently  on  the  young  branches  near  the  crotches.  The 
eggs  are  very  minute  and  appear  as  tiny  droplets  of  water  without 
any  definite  arrangement. 

Clarke5  described  the  egg  as  follows : 

"The  newly  placed  egg  is  pearly  white  and  shows  under  the  micros- 
cope a  rather  coarse  reticulation.  Before  hatching,  the  color  changes 
to  a  deep  yellow,  almost  orange  color  and  at  this  stage  the  egg  is  quite 
conspicuous.  It  is  about  two-fifths  of  a  millimeter  in  length  by  one- 
fifth  in  breadth,  being  a  rather  long  oval  in  shape,  about  twice  as  long 
as  broad." 


Fig.  9b. — Fruit  showing  characteristic  injury  to  plums  and  apricots. 


434  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Larvae  of  the  Second  Generation. — Between  June  5  and  June  10 
larvae  of  the  second  generation  appear  at  Davis.  These  larvae  attack 
fruit,  if  any  is  present  on  the  tree.  If  fruit  is  not  present,  they  bore 
into  the  shoots  in  the  same  manner  as  larvae  of  the  first  generation. 
Sometimes  they  may  feed  for  a  short  time  on  the  shoots  and  later 
go  into  the  fruit. 

In  the  majority  of  cases  the  larvae  enter  the  fruits  at  the  stem  end, 
probably  because  it  is  the  first  reached.  They  may  also  enter  through 
the  side  as  well,  especially  when  two  fruits  are  in  contact,  entrance 
being  made  at  the  point  of  contact.  After  gaining  entrance  through 
the  skin  they  begin  to  eat  out  the  flesh,  often  making  a  large  hole 
which  fills  with  a  gummy  substance,  (figs.  9a,  9b).  The  skin  above 
often  turns  black,  thus  indicating  the  presence  of  the  larva.  Injuries 
of  this  nature  account  for  the  name  "fruit  miner,"  as  the  insect  is 
sometimes  called.  Following  another  common  habit,  the  larva  works 
its  way  straight  to  the  pit,  and  if  the  latter  is  not  already  hardened, 
the  larva  will  bore  through  to  the  kernel  and  seems  to  eat  that  with 
relish.  This  is  one  cause  of  the  characteristic  "split  pits"  of  the 
stone  fruits.  When  the  larvae  have  penetrated  to  the  pit  their  pres- 
ence may  be  detected  by  small  bits  of  masticated  fruit  and  gum 
which  are  thrown  out  by  the  insect  on  the  surface  of  the  fruit  (figs. 
9a,  9b). 

In  either  case  the  injury  is  the  same,  the  fruit  being  rendered 
unsuitable  for  shipment  as  a  fresh  product  or  for  commercial  canning. 
The  California  Fresh  Fruit  and  Vegetable  Standardization  Act  for- 
bids the  packing  of  "wormy"  fruit  and  canners  refuse  to  buy  it. 
Therefore  many  fruit  growers  must  discard  large  quantities  of  in- 
fested apricots,  nectarines,  peaches,  and  plums  that  are  otherwise 
perfect.  It  is  not  an  uncommon  sight  to  see  ten  to  twenty  lug  boxes 
(each  forty  pounds  net)  of  "wormy"  fruit  culled  out  of  a  single 
packing-house  each  day  of  the  picking  season.  When  picking  the 
late  clingstone  peaches  in  certain  districts,  pickers  leave  enormous 
quantities  of  "wormy"  fruit  on  the  ground.  Most  growers  make  no 
attempt  to  salvage  this  fruit  while  some  prevent  complete  loss  by 
using  it  for  drying  or  home-canning. 

Larvae  of  the  Third  Generation. — Warren  T.  Clarke,  E.  0.  Essig, 
and  the  writer  have  made  careful  observations  and  have  secured 
evidence  of  a  distinct  third  generation  of  larvae.  During  the  season 
of  1921  serious  injury  was  evident  to  late  clingstone  peaches  in 
Placer  County,  California,  and  this  was  attributed  by  L.  H.  Day  of 
the  Division  of  Pomology  to  a  later  brood  of  larvae.  On  Septem- 
ber 30,  1921,  Day  stated  as  follows  in  correspondence: 


Bulletin  355]  THE  pEACH  TWIG-BORER  435 

"I  have  neglected  to  report  to  you  of  my  findings  in  regard  to  the 
peach  work  at  Newcastle.  I  went  up  there  a  week  ago  last  Tuesday. 
I  found  that  there  was  a  distinct  brood  of  the  twig-borers  which  had 
begun  to  hatch  about  three  weeks  before  that  date.  Evidently  many 
of  these  worms  on  hatching  had  immediately  gone  into  hibernation, 
while  others  were  attacking  the  fruit.  The  ones  that  were  in  hiberna- 
tion were  of  the  usual  small  size,  that  is  to  say,  %6  of  an  inch  long, 
while  those  that  were  feeding  in  the  peaches  would  average  around 
Ys  to  y±  of  an  inch  long. 

' '  There  were  a  few  growers  who  lost  50  per  cent  of  their  peaches  and 
the  Silva-Bergtholdt  people  lost  about  20  per  cent  of  their  Phillips 
Clings  and  Levi  Clings.  There  were  a  very  small  number  of  larger 
worms  ready  to  pupate  and  a  few  in  the  pupating  state.  A  few  evidently 
had  recently  emerged  as  adults.  On  the  ground  under  the  infested  trees 
were  quite  a  number  of  green  fruits  that  had  been  lying  on  the  ground 
for  some  weeks  and  in  which  there  had  been  larger  worms  which  evi- 
dently had  emerged  some  weeks  before.  This  seems  to  indicate  that 
there  was  a  distinct  brood  at  this  time.  I  found  quite  a  number  of  the 
hibernating  larvae  in  the  old  trees  and  in  a  nursery  just  over  the  fence 
from  an  infested  orchard  I  found  quite  a  large  infestation  of  the 
hibernating  larvae.  I  made  counts  in  a  few  trees  and  will  go  up  a 
little  later  and  make  another  count  to  see  if  there  has  been  an  increase 
in  the  infestation.  In  a  small  nursery  tree  I  found  12  hibernating 
larvae. 

"This  infestation  of  nursery  stock,  as  I  had  told  you  before,  is  not 
new,  as  I  have  often  found  several  dozen  hibernating  larvae  in  one 
nursery  tree.  Some  years  practically  all  nursery  stock  in  the  state 
contain  large  numbers  of  these  hibernating  larvae,  while  other  years 
there  will  be  practically  none,  or  very  few.  The  growers  reported  that 
there  were  practically  very  few  worms  in  the  midseason  peaches  such 
as  the  Elberta,  probably  as  much  as  1  or  2  per  cent  infestation.  Down 
at  Penryn,  which  is  at  a  lower  elevation,  Mr.  Butler  of  the  Penryn 
Fruit  Company  told  me  that  the  infestation  of  worms  began  a  little 
bit  earlier,  attacking  the  Orange  Clings  which  ripen  a  week  or  two 
earlier  than  the  Phillips. " 

Some  of  these  late  larvae  apparently  go  into  hibernation  while 
many  others  attack  the  fruit.  This  observation  is  substantiated  by 
Yothers36  in  Washington,  Wilson35  in  Oregon,  Clarke5  in  California, 
and  by  other  observers.  According  to  Clarke,  the  larvae  of  the  third 
generation  "are  the  only  ones  that  enter  the  fruit  immediately  on 
hatching" — that  is,  they  do  not  act  as  "twig-borers."  At  first  they 
make  very  minute  burrows  contrasting  strongly  with  the  freshly  made 
burrows  of  the  preceding  generation. 

Hibernation  of  Last  Brood  of  Larvae. — The  last  eggs  are  laid 
in  trees  in  the  vicinity  of  Davis  about  the  last  of  August,  as  far  as  our 
observations  indicate.  In  Placer  County,  Clarke  states,  and  Day  con- 
firms,  that   egg   laying   continues   well   into    September.      The   very 


436 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


minute  larvae  (fourth  generation)  from  these  eggs  begin  constructing 
hibernaculae  at  once  in  Yolo  County,  while  in  Placer  County  some 
of  them  eat  into  late  peaches  and  there  attain  considerable  size  before 
hibernating. 


Fig.  10. — An  important  natural  enemy  of  the  peach  twig-borer  is  another 
insect  which  devours  the  hibernating  larvae.  It  is  a  hymenopterous  parasite  named 
Eyperteles  lividus  (Ashmead).  Winged  adult  and  larva  shown  above.  (Original 
drawings.     Enlarged.) 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


437 


Parasitism. — In  most  sections  of  California  hibernating  larvae  of 
the  peach  twig-borer  are  attacked  by  natural  enemies.  During  the 
winter  1921-1922,  a  small  hymenopterous  larva,  Hyperteles  (Oxymor- 
pha)  lividus  (Ashmead),  (fig.  10)  was  found  destroying  from  70  to 
95  per  cent  of  the  immature  larvae  in  many  orchards.  The  parasite 
devours  the  body  of  the  larva  and  leaves  only  the  empty  head.  When 


Fig.  11. — Exit  hole  of  parasite  from  burrow  of  hibernating  larva.     (Enlarged.) 

the  parasite  has  accomplished  this  it  bores  its  way  out  through  the 
bark,  leaving  a  small  exit  hole  at  the  base  of  the  chimney  (fig.  11). 
The  original  description  of  this  parasite  by  Ashmead1  is  as  follows: 

"Male:  Length  .14  inch.  Uniform  dark  blue  including  legs,  ex- 
cepting the  first  three  tarsal  joints,  which  are  pale  or  white,  and  the 
upper  surface  of  the  thorax  which  has  a  greenish  metallic  tinge;  the 
antennae  are  black  and  hairy;  thorax  punctate,  abdomen  is  very  long 
and  slenderly  pointed;  wings,  hyaline,  with  pale  yellowish  veins,  the 
marginal  vein  is  long  and  thickened,  the  stegnal  short,  while  the  post- 
marginal  vein  is  long. 

Description  from  one  male  specimen  swept  from  bushes  in  a  low  swampy 
meadow. 

This  genus  was  found  by  Doctor  Furster  in  1856,  '  Hymenopterogische 
Studies  11,  Chalcidino  and  Proctorrupii,  p.  145, '  and  this  is  the  first  species 
described  in  our  fauna. " 


438 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


It  is  stated  by  Marlatt23  that  in  California  a  minute  mite  (Pedicu- 
loides  ventricosus)  destroys  from  75  to  95  per  cent  of  the  larvae. 
Professor  Clarke  was  "unable  to  confirm  the  statement  made  by 
Marlatt."     The  writer  has  not  seen  this  parasite  either. 

Lintner22  and  Comstock8  described  the  work  of  a  chalcid  parasite 
(Copidosoma  variegatum  Howard)  which  destroyed  the  pupae  of  the 
peach  twig-borer.  So  far  as  the  writer  could  learn,  thr  parasite  has 
not  been  found  in  California. 


Fig.  12. — Trees  inclosed  in  cheese-cloth  tents  for  the  purpose  of  making  life- 
history  studies.  (Photographs  taken  after  tents  had  been  torn  and  studies  com- 
pleted.) 


LIFE  HISTORY  EXPERIMENTS 

Evidences  of  a  Second  Generation. — As  previously  stated,  there 
have  been  conflicting  theories  regarding  the  number  of  generations 
of  the  peach  twig-borer.  Evidence  is  here  presented  to  prove  the 
existence  of  a  distinct  second  generation  (as  well  as  a  third  and  fourth 
proved  later  on),  rather  than  one  uneven  brood  that  extends  through 
the  season. 

A  few  investigators  claim  to  have  evidence  of  one  irregular  brood. 
Weldon34  found  newly  constructed  chambers  as  early  as  May  19 
in  Ventura  County,  on  June  23  in  San  Joaquin  County,  and  again  at 
Hanford,  Kings  County,  on  July  24.  On  the  basis  of  these  observa- 
tions he  concludes,  "the  presence  of  only  one  strung-out  brood  of 
this  insect,  instead  of  three  or  even  four,  as  have  been  previously 
reported. ' ' 

This  conclusion  may  be  misleading  since  it  is  highly  probable  that 
these  few  larvae  may  have  been  "freaks"  of  the  brood  that  carried 
over  in  a  single  generation,  while  the  great  majority  went  through 


Bulletin  355]  TIIE  PEACH  twig-borer  439 

two  or  three  generations.  "This  latter  supposition  would  also  ac- 
count for  the  existence,  during  the  winter,  of  larvae  of  different 
sizes,"  Wilson35  states. 

The  writer  has  followed  closely  the  life  history  of  the  peach  twig- 
borer  at  Davis  (fig.  12)  as  well  as  in  Placer  County  (fig.  13),  and  his 
findings  are  presented  under  "Life  History"  (p.  426).  Careful  counts 
were  made  on  each  of  562  almond  seedlings  at  the  University  Farm, 
Davis,  between  April  1  and  21  and  between  June  10  and  June  13, 


Fig.  13. — One  of  the  experimental  plots  in  Placer  County,  Sierra  Foothill 
District. 

respectively  (figs.  14  and  15).  The  counts  made  April  1-21  were 
primarily  to  determine  the  effectiveness  of  the  different  spray  treat- 
ments and  are  discussed  in  full  under  "Spraying  Experiments,"  (p. 
443).  In  making  the  counts,  the  wilted  tips  were  sought  and  opened 
to  reveal  the  larvae.  It  should  be  noted  that  the  unsprayed  trees 
had  an  actual  average  of  5.2  larvae  per  tree  at  this  time  (table  1). 

After  the  first  count  was  made  the  trees  were  observed  for  further 
wilting  of  the  shoots,  but  no  additional  infestation  could  be  found. 
The  wilted  twigs  dropped  off  and  new  lateral  shoots  were  sent  out 
in  their  place.  During  this  time  the  insects  were  observed  going 
through  their  pupation  and  emergence  as  adults. 


440 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


On  June  8  large  numbers  were  again  noticed  attacking  the  new 
shoots  on  the  same  trees.  The  second  count  was  then  made  in  the  same 
manner  as  the  first  (fig.  15).  The  significant  facts  are  that,  first, 
the  number  of  larvae  this  time  averaged  12.5  per  tree,  an  increase 
of  150  per  cent;  and  second,  the  infestation  was  general  throughout 
the  entire  orchard.  Sprayed  trees  which  at  the  first  count  had  no 
larvae,   contained   exactly   the   same   average,   i.e.,   12.5,   as   the  un- 


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Bulletin  355] 


THE  PEACH   TWIG-BORER 


441 


sprayed  trees.     The  infestation  had  been  spread  by  the  moths  flying 
about  the  orchard. 

In  addition  to  the  above  facts,  another  point  of  interest  was  that 
larvae  taken  at  the  same  time  from  peach  and  apricot  fruit  at  Winters 
(twelve  miles  west  of  Davis)  were  brought  to  Davis  and  placed  in 
jars,  indoors,  by  the  side  of  similar  jars  containing  infested  twigs 
taken  from  the  trees  at  Davis.  All  these  larvae  transformed  to  adults 
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Bulletin  355]  THE  PEACH  twig-borer  443 

time  of  emergency  is  almost  the  same  regardless  of  whether  the 
larvae  attacked  fruit  or  twigs. 

The  above  facts  and  figures  seem  to  afford  conclusive  evidence  that 
there  is  a  distinct  second  generation  of  the  peach  twig-borer. 

On  July  18  examination  of  the  orchard  revealed  no  twig  infesta- 
tion and  pupae  were  found  on  the  trunks.  Successive  examinations 
were  made  up  to  July  30,  but  no  larvae  were  found  in  the  twigs. 
It  is  important  to  note  that  at  this  time  the  terminal  growth  was  be- 
ginning to  harden,  which  probably  accounts  for  the  cessation  of 
infestation. 

Evidences  of  a  Third  Generation. — As  stated  under  "Life  His- 
tory" (p.  426),  there  is  a  distinct  third  generation  of  larvae,  as  proved 
by  experiments  at  Esparto  and  Newcastle.  The  following  observa- 
tions are  the  proof : 

Between  June  15  and  June  22,  12,496  apricots  and  plums  were 
examined  and  counted;  out  of  this  number  574  larvae  were  found, 
all  of  which  were  practically  full-grown  larvae  of  the  second  gen- 
eration. On  June  22  some  of  the  fruit  from  the  same  trees  showed 
infestation  of  newly  hatched  larvae  of  a  third  generation.  On  this 
date  Mr.  Hartwig,  owner  of  the  orchard,  reported  that  a  shipment 
of  75  crates  of  Formosa  plums  had  been  condemned  by  the  horti- 
cultural inspector  of  the  Winters  shipping  sheds  on  account  of  being 
infested  with  peach  twig-borer  to  the  extent  of  19  per  cent  of  the 
shipment.  Upon  investigation  it  was  discovered  that  this  fruit  was  in- 
fested with  newly  hatched  larvae,  which  apparently  had  hatched 
from  eggs  on  the  fruit  and  which  during  the  warm  period  had  de- 
veloped so  rapidly  that  the  injury  they  did  was  easily  seen  twenty-four 
hours  after  the  time  of  packing.  All  the  damage  was  the  work  of  very 
tiny  caterpillars  which  were  about  y10  of  an  inch  long. 

To  further  test  this  development,  the  writer  selected  250  perfect 
specimens  of  Formosa  plums  from  this  orchard  and  placed  them  in  a 
covered  lug  box,  which  was  left  at  Esparto,  and  brought  twenty-five 
similar  specimens  to  Davis.  These  fruits  were  examined  the  follow- 
ing day  and  newly  hatched  caterpillars  were  found  in  both  lots. 
Emergence  continued  for  four  days.  Of  the  250  apparently  worm- 
free  plums,  9  became  infested,  and  of  the  25  plums  brought  to  Davis, 
4  became  infested.    After  the  fourth  day  no  additional  larvae  hatched. 

W.  T.  Clarke  was  kind  enough  to  visit  the  Hartwig  orchard  in 
company  with  the  writer  to  examine  the  evidence  of  a  new  brood.  It 
was  his  unconditional  statement  that  this  injury  was  the  work  of  a 
distinct  new  generation. 


444  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Observations  similar  to  the  above  were  made  at  Newcastle  on  late 
clingstone  peaches.  It  is  interesting  to  note  that  the  third  genera- 
tion at  Newcastle  emerged  about  two  months  later  than  at  Esparto, 
apparently  on  account  of  climatic  differences. 


SPEAYING  EXPEKIMENTS,    1921 

Practically  all  the  experimental  data  on  the  control  of  the  peach 
twig-borer  have  been  secured  on  peach  trees;  very  little  work  has 
been  done  with  other  orchard  trees.     On  the  basis  of  results  secured 


Fig.  16. — Spraying  almond  trees  with  typical  power  outfit. 

on  peaches,  the  same  recommendations  have  been  made  for  the  other 
stone  fruits,  seemingly  with  the  same  results.  In  these  experiments 
it  was  therefore  thought  best  to  select  some  host  plants  that  had  not 
been  used  before. 

Fortunately  there  were  at  the  University  Farm,  Davis,  562  two- 
year  old  almond  seedlings  which  showed  heavy  infestation  in  1920. 
These  were  set  aside  for  the  spray  treatments  in  the  fall  of  1920  and 
were  not  sprayed  except  as  hereafter  described. 

C.  D.  Gregory  at  Winters,  Yolo  County,  offered  the  use  of  twenty- 
one  apricot  trees  (approximately  25  years  of  age)  to  be  used  in  the 
tests.  These  trees  had  been  examined  by  E.  R.  de  Ong,  of  the  Ento- 
mology Division,  and  reported  badly  infested  with  peach  twig-borer. 

The  use  of  a  third  block  of  trees  was  volunteered  by  J.  Caughy 
at  Vacaville,  Solano  County.     This  block  consisted  of  nine  hundred 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


445 


Wickson  plum  trees  which  every  year  had  produced  a  considerable 
amount  of  " wormy"  fruit. 

Details  of  the  Experiments. — The  almond  seedlings  at  Davis  were 
divided  into  rows  to  be  sprayed  and  rows  not  to  be  sprayed.  Approxi- 
mately every  third  row  crosswise  of  the  planting  was  set  aside  as  a 
check  row  and  three  successive  rows  at  right  angles  to  these  for  check 
trees,  (fig.  14).  This  gave  a  large  number  of  unsprayed  trees  for 
comparison  with  sprayed  trees.  A  series  of  spray  treatments  was 
outlined  to  test  various  materials  and  the  proper  time  for  applying 
them.  The  sprays  were  applied  by  the  writer  with  a  "Vermorel 
Eclair"  knapsack  sprayer.  Each  tree  was  given  a  thorough  coating 
over  the  entire  surface.  The  time  of  application  and  materials  used 
are  given  in  table  1. 


Table  2 
Summary  of  Spraying  Experiments,  1921,  University  Farm,  Davis 


Material  and  Type  of  Spray 


Trees  Dormant 
Per  Cent 
Control 


Buds  Swelling 
Per  Cent 
Control 


Full  Bloom 
Per  Cent 
Control 


Lime-Sulfur  ("Rex") 

Crude  Oil  Emulsion 

Distillate  Emulsion 

Spra-Mulsion 

Nicotine  Sulfate  plus  Hard  Soap  3 

Barium  Sulfur 

Dry  Lime-Sulfur 

Zinc  Arsenite 


96.7 
33.0 
12.0 
22.0 


74.4 
70.0 
10.0 
4.0 
97.4 
87.2 


46.7 

36.4 

6.0 

100.0 

18.0 

7.0 

100.0 


The  apricot  trees  at  Winters  were  divided  into  three  blocks.  To 
one  block,  liquid  lime-sulfur,  1  in  10,  was  applied  as  the  buds  were 
swelling,  and  dry  lime-sulfur,  12  to  50,  was  put  on  a  second  block 
at  the  same  time,  while  a  third  block  was  left  unsprayed.  The  sprays 
were  applied  with  a  power  sprayer  and  spray  guns  (fig.  16). 

The  plum  trees  at  Vacaville  were  likewise  divided  into  three 
blocks  and  subjected  to  the  same  sprays  as  the  apricot  trees  at  Winters. 
Spraying  here  was  also  done  with  a  power  sprayer  and  spray  guns. 

Counts  were  made  of  infested  twigs  and  infested  fruit  in  these 
orchards  and  the  results  are  tabulated  in  tables  1,  2  and  3.  Unfortu- 
nately, counts  in  the  Vacaville  orchard  were  vitiated  on  account  of  a 
high  north  wind  just  before  picking  time.  To  the  casual  observer 
there  was  a  difference  between  sprayed  and  unsprayed  blocks,  but 
no  counts  could  be  made  in  this  orchard  that  would  afford  accurate 
comparison. 


446 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Discussion  of  Results. — From  tables  1  and  2  we  note  the  following : 
(a)   Liquid  lime-sulfur  spray  has  given  from  46.7  to  96.7  per  cent 

control  of  the  first  generation  of  larvae.     Spraying  when  the  trees 

were  dormant  gave  the  best  control. 


Table  3 

Spraying  Experiments 

C.  D.  Gregory  Orchard,  Winters,  Counts  Made  June  22-28,  1921 
Dry  Lime-Sulfur  vs.  No  Spray 


Material 

Tree 

No. 

Number 
Infested  Fruits 

Total 

Infested 

Fruits 

Total  Fruits 
not  Infested 

Total 
Fruits 

Per  Cent 

On 
Tree 

On 
Ground 

Tree 

Ground 

of 
Infesta- 
tion 

No  Spray 

16 
17 

18 

7 

7 

21 

66 
16 
30 

73 
23 
51 

430 
174 

260 

180 
20 
66 

683 
217 
377 

10.6 

No  Spray 

10.1 

No  Spray 

13.5 

147 

864 

266 

1277 
Average 

11.4 

Dry  Lime- 
sulfur  

13 
14 
15 

7 
6 

7 

21 

10 

3 

28 
16 
10 

78 
79 
85 

130 
61 

58 

236 
156 
153 

11.4 
10.2 

(Pink  stage) 

6.5 

54 

242 

249 

545 

Average 
9.3 

Liquid  vs.  ] 

Dry  Lime-Sulfur 

Dry  Lime- 

1 

34 

25 

59 

352 

28 

439 

11.1 

sulfur 

2 

7 

27 
36 

15 

38 

42 
74 

466 
655 

35 
145 

543 

874 

7.7 

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8.6 

8 

50 

20 

70 

448 

41 

559 

10.7 

10 

29 

25 

54 

624 

38 

716 

7.5 

9 

32 

16 

48 

585 

40 

673 

7.1 

347 

3130 

327 

3804 

Average 

8.8 

Liquid  Lime- 

3 

7 

11 

18 

451 

19 

488 

3.7 

sulfur 

4 
5 

11 
10 

18 
13 

29 
23 

312 
318 

38 
22 

379 
363 

7.6 

(Pink  stage) 

6.0 

6 

4 

8 

12 

265 

20 

297 

4.0 

12 

16 

29 

45 

640 

30 

715 

6.2 

11 

14 

46 

60 

112 

6 

178 

3.3 

187 

2098 

135 

2420 

Average 

5.1 

Bulletin  355]  THE  peach  TWIG-BORER  447 

(b)  Dry  lime-sulfur  gave  control  inferior  to  that  of  liquid  lime- 
sulfur  when  applied  at  the  time  of  full  bloom. 

(c)  Nicotine  sulfate  resulted  in  excellent  control  both  at  the 
time  the  buds  were  swelling  and  at  full  bloom.  The  theory  is  that 
nicotine  sulfate  acts  as  a  mild  stomach  poison  as  well  as  contact 
spray,  thus  increasing  its  efficiency  as  an  insecticide. 

(d)  Zinc  arsenite  gave  as  perfect  control  as  nicotine  sulfate  when 
applied  during  full  bloom.  The  results  in  this  case  were  very  out- 
standing. On  not  a  single  sprayed  tree  could  a  caterpillar  be  found, 
while  adjoining  trees  were  heavily  infested  (fig  14).  As  the  larvae 
began  to  feed  they  were  quickly  killed  by  the  stomach  poison  awaiting 
them. 

(e)  Barium  Sulfur  (B.T.S.)  proved  to  be  a  good  control  remedy 
for  this  insect  when  sprayed  at  the  time  the  buds  were  swelling,  and 
of  little  value  at  the  time  of  blooming. 

(/)  Crude  oil  emulsion,  distillate  emulsion,  and  miscible  oil  (Spra- 
Mulsion)  were  not  at  all  effective  in  the  control  of  this  insect,  there 
being  in  many  cases  more  larvae  per  tree  on  sprayed  than  on  un- 
sprayed  trees. 

Referring  to  the  Winters  experiments  in  table  3  we  observe  that 
liquid  lime-sulfur  gave  somewhat  better  control  than  did  the  dry 
lime-sulfur,  and  both  were  a  slight  benefit  over  no  spraying. 

SPEAYING  EXPEEIMENTS,  1922 

The  spraying  experiments  of  1921  showed  some  very  interesting 
and  valuable  results  and  thus  furnished  the  basis  for  new  and  more 
extensive  experiments  in  other  sections  of  the  state  during  the  season 
of  1922. 

Placer  County  fruit  growers  were  very  eager  to  cooperate  in  the 
work  and  to  that  end  a  committee  was  appointed  at  the  Placer  County 
Fruit  Growers'  Convention  to  provide  ways  and  means  for  assisting 
the  University  in  its  investigations  of  the  peach  twig-borer  in  that 
district.  Meetings  were  held  with  members  of  this  committee  together 
with  R.  D.  McCallum,  farm  advisor,  and  C.  K.  Turner,  horticultural 
commissioner,  and  a  plan  of  work,  drafted  by  E.  0.  Essig  and  the 
writer,  was  adopted.  W.  H.  Cudaback,  assistant  farm  advisor,  was 
delegated  by  the  Division  of  Agricultural  Extension  to  arrange  the 
details  of  these  experiments. 

Likewise  in  Yolo  County,  W.  D.  Norton,  farm  advisor,  interested 
growers  in  setting  aside  blocks  in  their  orchards  for  experimental 
spraying. 


448 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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Bulletin  355] 


THE  PEACH   TWIG-BORER 


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Bulletin  355] 


THE  PEACH   TWIG-BORER 


451 


The  writer  repeated  and  enlarged  upon  the  1921  experiments  at 
the  University  Farm,  Davis,  and  on  test  plots  at  Vacaville  secured 
through  the  cooperation  of  growers  there. 

Details  of  the  Experiments. — The  spraying  experiments  at  Davis 
were  conducted  on  the  562  almond  seedlings  that  were  used  in  1921. 
The  planting  was  divided  into  check  rows  and  test  rows  which  were 
sprayed  at  different  stages  (fig.  17).  Counts  were  made  of  infested 
twigs  the  first  week  in  May  (table  4).  The  same  trees  were  again 
sprayed  on  May  11  to  combat  the  second  generation  of  larvae  and 
counts  were  made  early  in  June  to  determine  comparative  effectiveness 
of  the  spray  (fig.  18). 


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UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fourteen  plots  (fig.  13)  in  Placer  County  were  selected  for  the 
purpose  of  testing  those  materials  which  in  1921  proved  to  be  the 
most  promising.  Ten  trees  on  each  plot  were  set  aside  to  be  sprayed 
with  each  material  and  an  adjoining  row  of  ten  trees  was  sprayed 
in  the  pink  stage,  with  lime-sulfur  in  order  to  compare  the  test 
spray  with  the  standard  remedy.  Unfortunately,  in  only  a  few  cases 
could  unsprayed  trees  be  left  as  checks.  Counts  of  twig  and  fruit 
infestations  were  recorded  and  percentages  computed. 


Table  5 
Spraying  Experiments 
University  Farm,  Davis 
Summary  of  Results,  1921-1922 


Material  and  Type  of  Application 


Per  Cent  Control 

Per  Cent  Control 

1921 

1922 

96.7 

80.5 

25.0 

70.6 

74.4 

100.00 

41.66 

4.0 

43.0 

97.4 

95.5 

100.0 

46.7 

87.5 

7.0 

77.5 

6.0 

46.0 

100.0 

80.8 

100.0 

100.0 

100.0 

Trees  Dormant 

Liquid  Lime-sulfur 

Dry  Lime-sulfur 

Nicotine  Sulfate 

Buds  Swelling 

Liquid  Lime-sulfur 

Dry  Lime-sulfur 

Spra-Mulsion 

Nicotine  Sulfate 

Arsenate  of  Lead 

Full  Bloom 

Liquid  Lime-sulfur 

Dry  Lime-sulfur 

Spra-Mulsion 

Zinc  Arsenite 

Nicotine  Sulfate 

Arsenate  of  Lead 


The  H.  Hartwig  orchard  at  Esparto  was  selected  for  the  purpose 
of  comparing  the  effects  of  nicotine  sulfate,  arsenate  of  lead,  and 
lime-sulfur,  during  different  stages  of  blooming,  on  apricots,  peaches, 
and  plums.  Counts  of  infested  fruits  were  made  and  percentages 
of  control  compared. 

The  Winters  test  plots  were  on  the  A.  Wolf  skill  ranch  and  consisted 
of  lime-sulfur  and  arsenate  of  lead  sprays  on  apricot  and  plum  trees. 
Fruit  infestation  was  counted  as  in  the  other  plots. 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


453 


The  Vacaville  experiments  were  in  the  orchard  of  E.  I.  Power 
and  involved  nectarines,  peaches,  and  plums.  These  trees  were  sprayed 
with  lime-sulfur  plus  arsenate  of  lead  as  the  buds  were  swelling, 
and  also  received  a  second  spray  of  arsenate  of  lead  alone  on  May  11, 
for  the  purpose  of  controlling  the  second  generation  larvae.  Some 
trees  in  this  orchard  were  unsprayed,  while  others  received  only  one 
spraying  with  lime-sulfur. 


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UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Table  6 
Spraying  Experiments 
Placer  County— 1922 
Counts  of  infested  twigs  made  May  18,  1922 


Material  and  Type  of  Application 


Lime-sulfur  (Pink  stage,  3/17/22) 
Unsprayed 


Arsenate  of  Lead  (Full  bloom,  4/3/22) 
Unsprayed 


Bordeaux  Mixture  Arsenate  of  Lead 

(Pink,  3/23/22) 

Unsprayed 


Lime-sulfur  (Full  bloom,  4/4/22). 
Lime-sulfur  (Pink  3/22/22) 


Arsenate  of  Lead  (Pink  3/18/22).. 
Arsenate  of  Lead  (Pink,  3/18/22). 

Lime-sulfur  (Pink,  3/18/22) 

Lime-sulfur  (Pink,  3/18/22) 


Arseniteof  Zinc  (Pink,  3/20/22)4 

Arsenite  of  Zinc  (Full  bloom,  4/2/22). 

Nicotine  Sulfate  (Pink,  3/20/22) 

Nicotine  Sulfate  (Full  bloom,  4/2/22). 
Home-made    lime-sulfur-salt    (Pink, 

3/20/22) 

Unsprayed 


Lime-sulfur  (Pink,  3/22/22) 

Lime-sulfur  plus  Arsenate  of  Lead,  Hy- 

drated  Lime  Dust  (Pink,  3/22/22) 

Unsprayed 


Lime-sulfur,    plus    Arsenate    of    Lead 

(Pink,  3/20/22) 

Lime-sulfur  (Pink,  3/20/22) 


Nicodust  (Pink  3/22/22) 

Lime-sulfur  (Pink,  3/22/22). 


Nicodust  (Full  bloom,  4/4/22) 
Lime-sulfur  (Pink,  3/17/22) 


Orchard 


Van  Riper, 
Newcastle 


Silva-Bergtholdt, 
No.  3,  Newcastle 


E.  Appleton, 
Newcastle 


F.  Midgely, 
Newcastle 


H.  W.  Tudsbury: 
Newcastle 


C.  V.  Freed, 
Newcastle 


H.  E.  Butler, 
Penryn 


H.  N.  Hansen, 
Loomis 


J.  J.  Brennan, 
Loomis 


E.  L.  Rippey, 
Loomis 


No  of 
Trees 

No.  of 

Infested 

Twigs 

10 

6 

11 

74 

10 

0 

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9 

10 

0 

10 

10 

10 

24 

10 

18 

30 

13 

(Plums)  . 

10 

0 

(Peaches) 

10 

13 

(Plums) 

10 

4 

(Peaches) 

20 

10 

10 

21 

10 

16 

10 

38 

10 

48 

1 

20 

17 

0 

17 

0 

1 

0 

10 

1 

10 

4 

10 

0 

10 

5 

10 

20 

10 

2 

Average 
Infes- 
tation 


0.6 

6.7 

0 
0.9 

0 
1.0 

2.4 
1.8 

0.4 
0 

1.3 
0.4 

0.5 

2.1 
1.6 

3.8 

4.8 
20.0 


.1 

0.4 

0 
0.5 

0.2 
0.2 


Bulletin  355] 


THE  PEACH   TWIG-BORER 


455 


R.  Amaden  of  Dunnigan  and  E.  C.  Schrader  of  Arbuckle  con- 
ducted spraying  tests  in  their  almond  orchards  with  lime-sulfur  to 
compare  with  non-spraying.  The  infestation  in  these  orchards,  how- 
ever, was  so  slight  that  counts  were  abandoned. 

Millard  Sharpe  of  Vacaville  also  applied  various  spray  materials 
to  a  number  of  trees,  but  the  number  of  larvae  in  his  orchard  was 
so  small  as  to  make  the  experiment  of  little  value. 

Discussion  of  Results. — The  1922  experiments  did  not  result  in  as 
definite  comparisons  as  those  of  1921,  primarily  because  there  were 
so  few  larvae  in  unsprayed  trees.  Taking  this  into  consideration, 
we  must  limit  our  conclusions  somewhat. 

Results  of  the  Davis  experiments  are  shown  in  tables  4  and  5. 
Referring  to  these  results,  it  will  be  noted  that  lime-sulfur  has 
shown  itself  to  be  uniformly  good  in  controlling  the  twig  infestations 
at  all  stages.  Nicotine  sulfate  has  also  given  good  control,  results 
being  about  the  same  as  in  1921.  The  arsenicals  also  proved  valuable 
as  remedies  particularly  during  the  time  of  blooming.  Dry  lime- 
sulfur  was  in  all  cases  inferior  to  the  liquid  lime-sulfur.  The  oil 
sprays  were  not  at  all  effective. 


Table  7 
Spraying  Experiments 
Placer  County,  1922.     Counts  of  Infested  Fruits. 


Orchard 


Variety 
of  Peach 


Kind  of  Spray 


Condition  of 
Blossoms  at 

Time  of 
Application 


No.  of 
Trees 


Per 

Cent  of 
Loss 


1.  C.   V.   Freed  & 

R.  F.  Moss 

2.  Freed  &  Moss.... 

3.  H.  W.  Tudsbury 

4.  G.  Lammiman... 

5.  Freed  &  Moss.... 

6.  Freed  &  Moss.... 
Freed  &  Moss.... 
Freed  &  Moss.... 

7.  M.E.  Van  Riper 

8.  F.  Midgeley 

9.  J.  Brennan 

J.  Brennan 

10.  E.  L.  Rippey 

11.  H.  E.  Butler 

12.  H.  E.  Butler 

13.  E.  Appleton 

14.  H.  Hansen 


Tuscan 
Tuscan 
Elberta 

Levi 

Tuscan 

Tuscan 

Tuscan 

Tuscan 

Elberta 

Levi 

Phillips 

Phillips 

Elberta 

Levi 

Levi 

Salway 

Levi 


Nicotine  Sulfate   and 
Soap 

Nicotine  Sulfate  and  Soap 

Arsenate  of  Lead 

Arsenate  of  Lead 

Arsenite  of  Zinc 

Arsenite  of  Zinc 

Home-made  Lime-sulfur... 

Home-made  Lime-sulfur. . . 

Lime-sulfur 

Nicodust 

Lime-sulfur 

Nicodust 

Lime-sulfur 

Arsenate  of  Lead  (Dust)  .. 

Lime-sulfur 

Bordeaux  mixture  and  Ar- 
senate of  Lead 

Lime-sulfur  and  Arsen- 
ate of  Lead 


Pink 

Full  Bloom 

Pink 

Pink 

Pink 

Full  Bloom 

P.'nk 

Full  Bloom 

Pink 

Pink 

Pink 

Pink 

Full  Bloom 

Pink 

Pink 

Pink 

Pink 


10 
10 
10 
10 
10 
10 


10 

7 

10 
10 


34.5 
28.9 

0.2 

0.6 
20.8 
18.0 

0.5 
29.3 

1.0 


2.1 

4.3 
0.1 
0.8 
1.0 

0.1 

0.4 


456 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Table  8 
Summary  of  Spraying  Experiments,  H.  Hartwig  Orchard,  Esparto,  1922 


Kind  of  Fruit 

Type  of  Spray 

Date  of 

Date  of 

No.  Fruits 

No.  Fruits 

Per  Cent 

Spraying 

Count 

Examined 

Infested 

Control 

Apricots 

Lime-sulfur 

4/23 

6/15 

630 

30 

95.3 

(Royal) 

(Full  Bloom)  .... 

4/23 

6/15 

400 

9 

97.8 

I 

4/23 

6/15 

306 

15 

95.2 

4/23 

6/26 

351 

89 
Average 

74.7 

90.7 

(Formosa) 

(Full  Bloom)  .... 

4/24 

6/26 

297 
151 
454 
433 
237 

57 
154 
484 
533 
185 
196 
178 
167 
122 
346 

59 
446 
299 
543 
103 
170 

34 
10 
43 
66 
40 
18 
37 
47 
69 
36 
36 
36 
39 
13 
55 
13 
50 
49 
77 
19 
21 

88.5 
93.4 
91.5 
84.8 
83.2 
68.5 
76.0 
90.3 
87.1 
80.6 
81.7 
79.8 
76.7 
89.4 
84.2 
78.0 
88.8 
83.6 
85.9 
81.6 
87.7 

Nicotine  Sulfate 

4/19 

6/7 

349 

100 

42 
Average 
19 

88.0 

84-0 

Apricots 

81 

(Royal) 

(Full  Bloom) 

100 
100 
100 
500 
355 
486 
400 
178 
167 
200 
177 
500 
472 
774 

27 

24 

14 

79 

43 

21 

16 

3 

3 

7 

5 

26 

27 

37 

Average 

73 

76 

86 

84.2 

87.6 

95.9 

96 

98.3 

98.9 

96.7 

97.8 

94.8 

94.3 

95.1 

90.4 

Bulletin  355] 


THE  PEACH   TWIG-BORER 


457 


Table  8 — (Continued) 


Kind  of  Fruit 


Type  of  Spray 


Date  of 

Date  of 

No.  Fruits 

No.  Fruits 

Spraying 

Count 

Examined 

Infested 

4/19 

6/20 

1731 

61 

6/22 

300 

24 

6/28 

87 

5 

6/28 

737 

89 

6/28 

598 

80 
Average 

6/26 

138 

10 

6/20 

327 

36 

265 

28 

257 

20 

6/20 

437 

52 

Per  Cent 
Control 


Plums 
(Formosa) 


Nicotine  Sulfate 
(Full  Bloom) 


96.5 
92.0 
94.3 
88.0 
86.1 


91.0 


Apricots  (Royal) 

Plums 
(Formosa) 

Peaches 
(Alexander) 


Unsprayed. 
Unsprayed. 


Unsprayed. 


92.8 

89.0 
89.4 
92.3 

88.1 


From  figure  18  it  will  be  observed  that  the  second  generation  of 
larvae  was  reduced  by  both  arsenate  of  lead  and  nicotine  sulfate 
sprayed  about  May  15.  The  arsenate  of  lead  spray  reduced  the 
infestation  from  an  average  of  3.5  larvae  per  tree  in  the  unsprayed 
trees,  to  an  average  of  1.4,  while  nicotine  sulfate  reduced  the  average 
to  2.6. 

Tables  6  and  7  show  the  results  of  counts  on  the  fourteen  test  plots 
in  Placer  County.  Table  6  shows  the  effects  of  various  sprays  in 
reducing  twig  injury,  while  table  7  shows  the  per  cent  of  loss  of 
fruit.  It  is  unfortunate  that  unsprayed  trees  were  so  lightly  infested, 
yet  we  were  able  to  make  a  few  observations.  Lime-sulfur  seems  to 
be  a  satisfactory  spray,  particularly  when  the  application  is  made  at 
the  pink  stage.  The  arsenicals  and  nicotine  sulfate  also  proved  very 
effective  in  controlling  the  insect.  Addition  of  arsenate  of  lead  to 
either  lime-sulfur  or  Bordeaux  mixture  made  a  satisfactory  com- 
bination. Homemade  lime-sulfur  and  salt  in  these  tests  has  been 
inferior  to  commercial  lime-sulfur.  The  dry  dusts,  Nicodust  or 
arsenate  of  lead,  did  not  prove  good  remedies. 

In  the  Hartwig  orchard  at  full  bloom,  lime-sulfur  gave  90.7  per 
cent  control  on  apricots  (Royal)  and  84.0  per  cent  on  plums  (For- 
mosa). Nicotine  sulfate  gave  90.4  per  cent  and  91.0  per  cent,  respec- 
tively, on  the  same  kind  of  trees  at  full  bloom  (table  8). 

In  the  A.  Wolfskill  orchard  at  the  pink  stage  lime-sulfur  showed 
a  benefit  of  98.8  per  cent  on  apricots,  while  arsenate  of  lead  showed 
the  same  per  cent  control  on  plums  at  full  bloom,  and  on  peaches 
in  the  pink  stage  it  gave  96.8  per  cent  control  (table  9). 


458 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Table  9 
Summary  of  Spraying  Experiments,  A.  Wolfskill  Orchard,  Winters,  1922 


Kind  of  Fruit 

Type  of  Spray 

Date  of 
Spraying 

Date  of 
Count 

No.  Fruits 
Examined 

No.  Fruits 
Infested 

Per  Cent 
Control 

Apricots 

(Royal) 

Lime-sulfur 

(Pink  stage) 

Arsenate  of  Lead 
(Full  Bloom)  .... 

Arsenate  of  Lead 
(Pink) 

4/1 

4/1 

4/1 

6/16 
6/16 
6/20 

6/20 

6/28 
8/16 

1200 

1000 

500 

1820 

5000* 
2000 

81 
2 
0 
1 

Average 
62 

63 

92.3 

99.8 
100.0 
99.05 

98.8 

Plums 

(Formosa) 

Peaches 

(Elberta) 

98.8 
96.8 

*  Estimated. 

Table  10 
Summary  of  Spraying  Experiments,  E.  I.  Power  Orchard,  Vacaville,  1922 


Date  of 

Date  of 

No.  Fruits 

No.  Fruits 

Per  Cent 

Kind  of  Fruit 

Type  of  Spray 

Spraying 

Count 

Examined 

Infested 

Control 

Nectarines 

Lime-sulfur  and 

(Cardinal) 

Arsenate  of  Lead 

(Buds  swelling)  .. 
Arsenate  of  Lead.. 

2/20) 

5/11/ 

7/19 

9500* 

20 

99.8 

Unsp  rayed 

75.0* 

Nectarines 

Unsprayed 

7/19 

1050 

275 

74.0 

(Quetta) 

Unsprayed 

7/19 

75.0* 

Peaches 

Unsprayed 

8/10 

60.0* 

(Elberta) 

Lime-sulfur  and 
Arsenate  of  Lead 
(Pink) 

8/10 

98.0* 

Nectarines 

Lime-sulfur 

(Quetta) 

(Buds  swelling)  .. 
Arsenate  of  Lead 

2/15) 
5/25/ 

7/17 

26980* 

100 

99.7 

Arsenate  of  Lead.. 

5/25 

8/5 

35000* 

3 

99.02 

Unsprayed 

8/5 

300 

27 

91.0 

Peaches 

Arsenate  of  Lead 

5/15 

6/9 

200 

0 

100.0 

(Alexander) 

(Summer  spray) 
Arsenate  of  Lead 

200 
200 
200 

0 
0 

2 

100.0 

100.0 

98.0 

(Summer  spray) 

5/25 

7/17 

26980* 

100 

99.7 

*  Estimated. 


Bulletin  355]  THE  PEach  TWIG-BORER  459 

The  experiments  conducted  by  E.  I.  Power  at  Vacaville  were 
remarkable  in  showing  the  outstanding  benefit  of  lime-sulfur  and 
arsenate  of  lead  in  the  pink  stage,  and  of  arsenate  of  lead  in  the 
early  summer  for  the  second  generation  of  larvae  (table  10).  Power 
stated  that  he  had  never  been  able  to  produce  worm-free  nectarines 
before,  and  in  these  tests,  with  arsenate  of  lead  and  lime-sulfur 
and  a  summer  spray  of  arsenate  of  lead  alone,  he  was  able  to  secure 
99.8  per  cent  control  on  nectarines,  also  on  peaches.  In  these  tests 
arsenate  of  lead  proved  beyond  a  doubt  that  it  will  give  perfect  con- 
trol when  used  as  a  summer  spray  on  early  and  mid-summer  varieties 
of  nectarines  and  peaches. 


CONCLUSIONS 

The  habits  of  the  peach  twig-borer  have  been  studied  and  its  life 
history  carefully  worked  out.  Evidence  has  been  secured  which  proves 
the  existence  of  distinct  second  and  third  generations  and  sometimes 
even  a  fourth,  rather  than  one  uneven  brood,  as  heretofore  believed. 
New  features  in  control  measures  have  been  ascertained  which  make  it 
possible  to  successfully  combat  the  attacks  of  this  pest. 

In  these  experiments  nicotine  sulphate,  %  of  a  pint  to  100  gallons 
of  water,  with  three  pounds  of  soap  as  a  spreader,  gave  the  most 
consistent  and  highest  control  of  the  peach  twig-borer.  Arsenate  of 
lead,  3  pounds  to  100  gallons,  with  %  of  a  pound  of  casein  spreader, 
gave  excellent  control  at  the  pink  and  full  bloom  stages,  as  well  as  a 
summer  spray.  Liquid  lime-sulfur,  1  in  10,  was  very  satisfactory 
at  all  stages,  being  best  at  the  pink  stage.  For  the  full  bloom  stage, 
arsenate  of  lead  added  to  lime-sulfur  increased  the  efficacy  of  the 
latter.  Bordeaux  mixture  and  arsenate  of  lead  sprayed  just  before 
blossoming  time  proved  to  be  a  satisfactory  combination.  The  home- 
made lime-sulfur  and  salt  mixture  in  these  experiments  was  inferior 
to  the  commercial  preparation.  The  dry  dusts  and  the  oil  sprays  are 
not  satisfactory  remedies  for  this  pest. 

On  account  of  the  presence  of  a  natural  parasite,  Hyperteles  livi- 
dus  (Ashmead),  hibernating  larvae  in  certain  years  have  been  almost 
completely  eradicated  in  some  districts. 

Most  of  the  damage  of  the  peach  twig-borer  is  caused  by  larvae  of 
the  second  and  third  generations.  The  present  trouble  arising  from 
these  later  generations  is  due  to  a  number  of  factors,  chief  of  which 
are  the  lack  of  uniform  control  of  the  first  generation  and  failure 
to  destroy  or  properly  dispose  of  "wormy"  fruit  and  pruning  brush. 


460  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


KECOMMENDATIONS 

On  the  basis  of  the  foregoing  observations  and  experiments  and 
from  discussions  of  this  subject  with  Essig  and  others,  the  writer 
suggests  the  following  remedies  for  the  peach  twig-borer. 

1.  Spray  with  commercial  liquid  lime-sulfur  at  the  rate  of  1 
gallon  to  9  of  water,  plus  basic  arsenate  of  lead  powder,  3  pounds 
to  100  gallons,  in  the  spring  at  the  pink  stage,  that  is,  just  previous 
to  blossoming.  This  combination  will  control  diseases  and  insect 
pests  other  than  the  peach  twig-borer.  Because  of  the  frequent  damage 
resulting  from  lime-sulfur  in  coastal  districts,  it  is  considered  best 
not  to  use  this  spray  on  apricots.  Therefore,  Bordeaux  mixture, 
plus  basic  arsenate  of  lead,  3  pounds  to  100  gallons,  seems  to  be 
the  best  combination  on  apricots  when  brown  rot  or  shot  hole  fungus 
and  peach  twig-borer  are  to  be  controlled.  This  latter  spray  also 
should  be  applied  at  the  pink  stage. 

2.  Nicotine  sulfate,  %  of  a  pint  to  100  gallons  of  water,  with  3 
pounds  of  soap  as  a  spreader,  is  a  good  remedy  for  the  peach  twig- 
borer,  and  may  be  used  alone  in  a  few  limited  cases  where  diseases 
and  other  insects  are  not  troublesome. 

3.  A  summer  spray  of  arsenate  of  lead,  basic  or  neutral  (never 
acid),  at  the  rate  of  3  pounds  to  100  gallons  of  water  with  %  pounds 
of  casein  spreader,  may  be  used  as  an  additional  insurance  against 
"wormy"  fruit.  This  spray  should  be  applied  not  less  than  two 
weeks  before  the  fruit  is  picked. 

4.  Too  much  emphasis  cannot  be  placed  upon  the  necessity  of 
proper  spraying  at  the  right  time.  It  is  essential  to  cover  the  entire 
surface  of  the  tree,  particularly  the  newer  and  outer  portions  of  the 
branches.  Use  at  least  175  pounds  pressure  and  preferably  250 
pounds. 

5.  All  prunings  should  be  collected  and  particularly  the  small  and 
newer  wood  should  be  burned  before  spring,  because  this  material 
harbors  the  larvae. 

6.  Cull  fruit  should  not  be  carelessly  left  about  the  orchard  or 
packing  house.  All  wormy  fruit  should  be  collected  and  properly  dis- 
posed of.  It  should  be  fed  promptly  to  pigs  or  other  stock,  or  de- 
stroyed by  burying  or  burning.  A  quick  and  simple  manner  of 
destroying  worms  in  the  cull  fruit  is  to  place  the  discarded  fruit  in 
a  pile  or  in  a  trench,  saturate  with  oil  or  cover  with  wood,  and  ignite. 
The  resulting  heat  from  the  fire  will  be  sufficient  to  kill  the  larvae  in 
the  fruit.    Another  means  is  to  boil  the  fruit  for  fifteen  minutes. 


Bulletin  355]  THE  peach  TWIG-BORER  461 


SUMMARY 

1.  The  peach  twig-borer  (Anarsia  lineatella  Zeller)  is  a  serious 
pest  in  deciduous  orchards  of  California. 

2.  The  injury  is  caused  by  the  larvae  boring  into  the  buds,  twigs 
and  fruit  of  the  almond,  apricot,  nectarine,  peach,  plum,  and  prune. 

3.  The  insect  passes  the  winter  in  the  larval  stage  underneath  the 
bark  in  small  burrows  constructed  in  the  crotches  of  young  branches. 
In  early  spring  the  larvae  come  out  and  begin  feeding  on  the  buds 
and  shoots. 

4.  When  the  insects  are  full  grown  they  crawl  down  the  branches 
to  the  trunk  where  they  pupate  in  the  curls  of  the  rough  bark.  The 
adult  moths  emerge  in  early  summer  and  begin  egg  laying  on  the 
twigs. 

5.  About  the  first  week  in  June  a  second  generation  of  larvae 
begins  to  attack  the  twigs  and  particularly  the  fruit. 

6.  Later  in  the  summer  a  third  generation  emerges  in  some  sec- 
tions and  causes  serious  injury  to  late  ripening  varieties  of  the  fruits 
attacked. 

7.  The  fourth  and  last  generation  of  larvae  comes  out  late  in 
September  and  begins  at  once  to  construct  chambers  and  go  into 
hibernation  for  the  winter.  These  are  also  known  as  the  first  gene- 
ration larvae  of  the  following  year. 

8.  A  parasitic  larvae,  Hyperteles  lividus  (Ashmead),  has  been 
found  in  certain  districts.  In  some  seasons  it  destroys  as  high  as 
95  per  cent  of  the  hibernating  larvae. 

9.  Results  of  spraying  experiments  show  that  this  insect  can  be 
controlled  by  a  number  of  materials  and  at  different  times. 

10.  Nicotine  sulfate  and  arsenate  of  lead  have,  in  these  experi- 
ments, proved  to  be  slightly  better  than  lime-sulfur  in  controlling  this 
pest,  but  in  view  of  the  fact  that  lime-sulfur  is  an  all-round  fungicide 
and  insecticide,  it  is  advisable  to  use  lime-sulfur  at  the  pink  stage 
of  the  opening  buds,  with  the  addition  of  arsenate  of  lead  in  serious 
attacks. 

11.  Bordeaux  mixture  and  arsenate  of  lead,  applied  at  the  pink 
stage,  is  considered  best  on  apricots  in  the  coastal  region  because  of 
the  danger  of  lime-sulfur  injury  to  the  fruit. 

12.  The  lime-sulfur  substitutes  controlled  the  worms  less  per- 
fectly than  the  commercial  liquid  lime-sulfur.     The  oil  sprays  and 


462  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

the  dry  dusts  cannot  be  considered  satisfactory  remedies  for  this 
insect.  Arsenate  of  lead  applied  as  a  summer  spray  has  proved  very 
efficacious  on  almonds,  nectarines,  and  peaches. 

13.  Stress  is  placed  upon  spraying  at  the  proper  time  and  upon 
thorough  application. 

14.  Spraying  must  be  supplemented  by  proper  disposal  of  prun- 
ings  and  of  cull  fruits,  because  they  aid  in  carrying  over  the  insect 
from  one  generation  to  another. 


ACKNOWLEDGMENTS 

The  writer  wishes  to  express  his  gratitude  to  E.  0.  Essig  for  his 
valuable  advice  and  assistance  and  especially  for  reading  and  correct- 
ing the  manuscript  of  this  bulletin.  W.  L.  Howard  also  has  been 
exceedingly  helpful  in  making  valuable  corrections  to  the  manuscript. 
The  assistance  and  cooperation  of  W.  P.  Tufts  have  largely  con- 
tributed to  the  success  of  this  project.  A  great  many  useful  sug- 
gestions have  been  contributed  by  W.  T.  Clarke,  E.  R.  de  Ong,  and 
L.  H.  Day  which  have  been  valuable  in  the  completion  of  this  in- 
vestigation. Miss  Edna  Russ  and  W.  C.  Mathews  have  been  particu- 
larly helpful  in  making  charts  and  photographs.  Valuable  assistance 
has  also  been  rendered  by  members  of  the  Division  of  Pomology,  and 
by  R.  D.  McCallum,  C.  K.  Turner,  W.  H.  Cudaback,  and  W.  D. 
Norton. 


LITERATURE  CITED 

1  ASHMEAD,   W.   H. 

1886.     Trans.  Am.  Entom.  Soc,  vol.  13,  p.  135. 

2  Barnes,  S.  B.  and  McDunnough,  J. 

1917.     Check  List  of  Lepidoptera  of  Boreal  America,  p.  159. 

s  Chambers,  V.  T. 

1872.     Canadian  Entomologist,  vol.  4,  p.  208. 

4  Chambers,  V.  T. 

1878.     U.  S.  Geol.  and  Geog.  Surv.  Terr.,  Bull.,  vol.  4,  pp.  112,  129. 

s  Clares,  W.  T. 

1902.     The  Peach  Worm,  Calif.  Agr.  Exp.  Sta.,  Bull.  144. 

e  Clemens,  Dr.  B. 

1860.     Proc.  Acad.  Nat.  Sci.,  Philadelphia,  p.  169. 

7  Clemens,  Dr.  B. 

1872.     Tineina  of  North  America   (Stainton  edition),  p.  128. 


Bulletin  355]  TnE  PEACH  TWIG-BORER  463 


1878.  Proc.  West  N.  Y.  Hort.  Soc,  p.  13. 

9  COMSTOCK,    J.    H. 

1879.  Report  U.  S.  Dept.  of  Agr.,  p.  255. 

10  COQUILLET,  D.  W. 

1891.     Insect  Life,  vol.  6,  p.  206. 

11  CORDLEY,   A.    B.. 

1897.     Oregon  Agr.  Exp.  Sta.  Bull.  45,  p.  123. 

12  CORDLEY,   A.    B. 

1897.  U.  S.  Dept.  of  Agr.,  Div.  Ent.,  Bull.  9,  pp.  71-75. 

is  Craw,  A. 

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